My defense is that there have been more important things to cover. With Donald Trump and Hillary Clinton going at it head to head for the past four months, why waste valuable time on the undercard? Going into Tuesday night’s Vice-Presidential debate between Kaine and Pence, which will be held at Longwood University, in Farmville, Virginia, several answers present themselves.

The most obvious one is that, statistically speaking, there is a real possibility that either Kaine, the junior U.S. senator from Virginia, or Pence, the governor of Indiana, will eventually become President. Starting with John Adams, who succeeded George Washington in 1797, fourteen Veeps have moved up to the top job. In eight of these cases—Lyndon Johnson was the most recent—the sitting President got ill and died, or was assassinated. Three other Veeps—Thomas Jefferson, Martin Van Buren, and George H. W. Bush—were elected to the Presidency immediately after serving under their predecessors. Richard Nixon became President eight years after he left the Vice-Presidency, and Gerald Ford was forced to take over after Nixon resigned.

At the age of seventy, Trump would be the oldest President ever elected to office. Clinton, who will turn sixty-nine later this month, would be the second oldest, behind Ronald Reagan. The actuarial tables cannot be ignored, and neither can the possibility that the winner in November will serve a single term and then be succeeded by her or his No. 2. When viewers tune in to the debate on Tuesday night, they should be asking whether Kaine and Pence have what it takes to be President.

If the answer is negative, it could damage either party’s ticket as a whole. On October 5, 1988, in Omaha, Nebraska, I attended the Vice-Presidential debate between Lloyd Bentsen and Dan Quayle, a verbally challenged second-term senator from Indiana who looked a good deal younger than his forty-one years. Judy Woodruff, of what was then the “MacNeil/Lehrer NewsHour,” went straight at Quayle, pointing out that even Bob Dole, his leader in the Senate, had said a better qualified person could have been chosen.

Pointing to his experience on the Senate Budget and Armed Services committees, Quayle tried to defend himself. Later in the debate, he claimed to have “as much experience in the Congress as Jack Kennedy did when he sought the Presidency.” That gave the courtly Bentsen, who was twenty-six years Quayle’s senior, the chance to deliver what is perhaps the most famous zinger in debate history: “Senator, I served with Jack Kennedy. I knew Jack Kennedy. Jack Kennedy was a friend of mine. Senator, you’re no Jack Kennedy.” The next morning, on his campaign plane, Quayle still looked stunned. (Though, of course, George H. W. Bush and Quayle still won that November.)

It’s doubtful that we’ll see that kind of drama tonight. Kaine and Pence are both experienced politicians in their late fifties, and they both have a lot more wits about them than Quayle did. If either makes a major gaffe or misstep, it will be surprising. But in addition to demonstrating that they could step into the Oval Office if necessary, they both have important political tasks to carry out, particularly Pence.

Kaine’s job is to follow Clinton’s example from last week’s Presidential debate and keep up the pressure on Trump. He knows this. “It really is more about Donald Trump than it is about Governor Pence,” he told reporters recently. And he also said, “If I talk too much about Tim Kaine during my debate, I’m wasting my time.”

Since late July, when he was selected as Clinton's running mate, Kaine has had plenty of practice criticizing Trump. He’s called the Republican “an idiot” and “a one-man wrecking crew.” He’s drawn attention to what he’s called Trump’s “cozy bromance” with Vladimir Putin. He's even accused him of “pushing ... Ku Klux Klan values.” In addition to attacking Trump, Kaine is likely to spend a good deal of time speaking about Clinton's agenda to raise wages, make college more affordable, and expand childcare and other programs for working families. He has the advantage of coming from the same wing of the Democratic Party as Clinton—they both speak the same language of expanding opportunity, while modestly raising taxes on the rich and encouraging businesses, particularly small businesses, to grow.

Pence, on the other hand, has a number of philosophical differences with his running mate. He hails from the Paul Ryan wing of the Republican Party, which, at least until recently, supported globalization, free trade, and immigration reform. A favorite of the religious right, Pence is a social conservative who takes a hard line on issues like abortion and gay marriage. Trump, despite tacking to the right on a number of matters in recent years, rarely emphasizes social issues. During the campaign so far, however, the Indiana governor has done a pretty effective job of masking these divides and acting as a bridge between Trump and Party regulars. His game plan for Tuesday night will be to carry on in this vein, and to try to shift the campaign narrative back onto questions about Clinton.

To do that, he’ll have to fend off some questions about Trump, whose tax affairs and attacks on Alicia Machado, the former beauty queen who won his Miss Universe pageant, have dominated the news in the past week. The moderator, Elaine Quijano, of CBS News, will likely bring these stories up. Even if she doesn’t, Kaine surely will, and Pence will be forced to respond. “I think Mike Pence will need to come in and quickly dismiss those attacks and pivot to the problem of Hillary Clinton,” Scott Walker, the Republican governor of Wisconsin, told an interviewer on Sunday.

Walker should know. During some of Pence’s practice sessions for the debate, he played the role of Kaine, and he must have heard some of what Pence is planning to say. A key question is just how far Pence, who has a reputation as a low-key and mild-mannered fellow, will go in his role as attack dog. He will surely bring up the issues of Clinton’s e-mail server, the Clinton Foundation, and Benghazi—the latter two of which Trump, inexplicably, failed to mention during his first debate with Clinton last week. But will Pence venture beyond these well-trodden paths into areas such as Clinton’s marital history, which Trump has brought up repeatedly in recent days, and which was the subject of a long story in the Timespublished on Monday?

My guess is that Pence will leave this stuff to Trump; but he certainly won’t go easy on Clinton. Last month, he called her “the most dishonest candidate for President of the United States since Richard Nixon.” Tonight, we can expect to hear more along these lines, just as we will surely see Kaine going after Trump hammer and tongs. Which brings me back to where I started. This election is about Clinton versus Trump—everything else is a sideshow.